甲胎蛋白促使人肝癌细胞逃避淋巴细胞的攻击.pdf

Effects of alpha fetoprotein on escape of Bel 7402 cells from attack of lymphocytes1 Mengsen Li Sheng Zhou Department of Biochemistry Department of Biochemistry Hainan Medical College Hainan Medical College Haikou 570102, China Haikou 570102, China mengsenli@ mengsenli@ Xinhua Liu Pingfeng Li Department of Biochemistry and Molecular Biology Department of Biochemistry and Molecular Biology Peking University Health Science Center Peking University Health Science Center Beijing 100083, China Beijing 100083, China ligang55@ ligang55@ Gang Li Department of Biochemistry and Molecular Biology Peking University Health Science Center Beijing 100083, China ligang55@ Abstract Involvement of AFP against apoptosis of tumor cell has been implicated in its evasion of immune surveillance. However, the molecular events of immune escape mechanisms are still unknown. The major observations reported here relate to a possible mechanism by which heptoloma Bel 7402 cells escape immune surveillance in vitro. Western blotting and a well-characterized cofocal scanning image were performed to analyze the expression of Fas/FasL and caspase-3 in co-cultured Bel 7402 and Jurkat cells. After co-culture with Jurkat cells, up-regulated Fas and reduced FasL expression could be observed. Treatment with AFP could remarkably inhibit the elevated Fas and, whereas, induce the FasL expression in co-cultured Bel 7402 cells. Cells co-culture could induce the expression of caspase-3 in both cells line. The elevated caspase-3 in Bel 7402 cells was abolished following the treatment of AFP. The expression of caspase-3 was elevated in co-cultured Jurkat cells treated with AFP. No detectable change on the expression of survivin was examined in both cells line. Mono-antibody against AFP treatment alone did not obviously influence the growth of cells, as well as the expression of Fas/FasL and caspase-3. However, the effect of AFP could be 1. Supported by the National Natural Science Foundation of China (No.30271174 and 30260117). blocked by antibody. Our results provide evidence that AFP could promote the death of lymphocytes and the escape of liver cancer cells from immune surveillance through caspase signal pathway and the Fas/FasL interaction between liver cancer cells and immune cells. Key words: alpha fetoprotein, hepatoma, lymphocytes, immune escape, immune surveillance 1. Introduction Alpha fetoprotein (AFP) is one of several oncofetal proteins synthesized in large amounts by the fetus and drops in serum markedly shortly after birth. AFP as a tumor-associated fetal protein has demonstrated clinical utility as a tumor marker. Besides its role as a carrier or transporter for various serum ligands including fatty acids, retinoids, steroids, drugs, dyes and heavy metals, AFP has been reported to display growth regulatory properties. Previous studies have verified that AFP appears to functions as a growth regulator rather than only serum carrier. Multitude of cell types involving the growth and differentiation effects of AFP include placental [1], lymphoid [2], ovarian [3], uterine [4], gastric cancer [5], epidermal [6], breast cancer [7] and fetal fibroblasts [8]. Recently, some studies on the mechanisms of AFP suggested that AFP induced apoptosis in tumor cells independently of Fas/Fas ligand or TNFR/TNF signaling pathway, and AFP-mediated cell death involved activation of the effector caspase-3-like proteases, but was independent of upstream activation of the initiator caspase-1, caspase-8, and caspase-9-like proteases [9]. The intracellular mechanism of AFP involving to cAMP-PKA signaling pathway after its binding to different affinity receptors has been also reported [10]. Although the biological roles of the oncoembryonal protein AFP, including immunoregulatory functions in a variety of immune responses including the humoral and cell-mediated types, have been reviewed in detail, the evidences for the role of AFP in hepatoma cells escaping from host immune surveillance are still unknown [11-12]. In a recent study, AFP was used as an effective tumor rejection antigen to observe its effect in T-cell immune responses, implicating a gene therapy-based strategy for hepatoma cells [13]. However, the over-expression of AFP in human hepatoma cells is concurrent with aberrant growth manifestation. We presume that the altered serum AFP level is the cause of such changes rather than a coincident phenomenon and should be responsible for the malignant progression of liver cancer. Thus revealing the intracellular mechanisms underlying the evasion of tumor from host immune surveillance will provide further insights i。